This invention relates to a latch construction of the type in which a rotatable crank hub drives a bolt between extended and retracted positions through a driving lever or levers having a rearward end pivotally connected to a crank arm of the crank hub through a transverse driving pin and a forward end pivotally connected to the bolt. Furthermore, as the bolt moves into and is placed in the extended position, the driving pin between the crank arm and the driving lever or levers is located in a slot of the latch frame so as to resist outside rearward forces against the bolt attempting to move the same from its extended position. According to the improvements of the present invention, a resilient force is exerted against cam means on the crank hub resiliently urging the driving pin into the frame slot and resiliently resisting removal from the frame slot as the bolt approaches and moves into extended position, thereby more positively insuring the intended functioning of the driving pin and frame slot engagement.
Various prior latch constructions have heretofore been provided wherein it has been attempted to positively secure the bolt thereof in extended position in an effort to frustrate surreptitious attempts at driving the same by use of an outside force from such extended position. For instance, door-mounted latch bolt constructions, usually deadbolt constructions for maximum security, have the bolt thereof in extended position received in a keeper of the door frame. When attempts are made to violate the security of the dead-bolt construction, one of the major areas of attack is against the extended bolt by penetrating either the opening between the door and door frame or directly through the door frame, in both cases applying forces directly against the bolt in an effort to drive it from its extended position toward its retracted position. In an effort to frustrate this bolt driving form of attack, means is provided in addition to the normal bolt moving mechanism for securely retaining the bolt in its extended position, once placed therein, and against this outside force attack thereagainst.
One prominently used prior deadbolt construction having this security increasing means integrated therein has included a rotatable crank hub movable by transversely connected exterior lock and interior lock or hand operators, the crank hub having a radially projecting crank arm which is end pivotally connected to the rearward end of a longitudinal driving lever or levers. The forward end of the driving lever or levers is, in turn, pivotally connected to the rearward end of a usual longitudinally slideable bolt. Thus, limited rotation of the crank hub in one direction moves the bolt from a retracted position totally within a bolt casing longitudinally forwardly to an extended position projecting a determined distance from the bolt casing, and reverse limited rotation of the crank hub similarly moves the bolt from such extended back to its retracted position.
The means for providing the described increased security in the bolt extended position is arranged in conjunction with the pivotal connection between the crank arm of the crank hub and the driving lever or levers. A transversely extending driving pin is used for this pivotal connection and generally vertical slots in the latch frame are located so that when the crank arm and driving lever or levers are moved longitudinally forwardly to place the bolt in its extended position, the final location of the bolt in its extended position also locates this driving pin in the latch frame slots. The overall result is that with the bolt in extended position placing the driving pin in the frame slots, any attempted rearward driving force against the bolt is transmitted longitudinally rearwardly into the driving lever or levers, rearwardly into the driving pin between the driving lever or levers and the crank arm and directly into the slotted latch frame so that the rearward driving force is resisted by the latch frame retaining the bolt extended.
In order to assure that the driving pin always locates fully within the frame slots in the bolt extended position, a spring has been positioned at the pivotal connection between the forward end of the driving lever or levers and the rearward end of the bolt. This spring is positioned such that it tends to urge the operating lever or levers to pivot in proper direction relative to the bolt so that the rearward end of the operating lever or levers, and thus the driving pin is always urged into the frame slots as the bolt approaches its fully extended position. Thus, this spring urged pivoting force at the forward end of the driving lever or levers which is transmitted rearwardly through the driving lever or levers into the driving pin always assures that the driving pin will locate fully within the frame slots when the bolt reaches its fully extended position.
One of the principal difficulties with this prior latch bolt construction in which the security insuring spring is at the forward end of the driving lever or levers is the distance thereof from the driving pin, the motion of which it is required to insure. Obviously, the efficiency of these relatively widely spaced elements is somewhat suspect. Unless the spring, the key to the overall combination, is precisely formed and precisely positioned, the intended result could be partially or totally frustrated.
Other prior latch bolt constructions of similar form have attempted to provide the desired security by use of a different form of spring located in a different manner. A leaf spring is positioned in the latch frame extending longitudinally over the entire of the driving lever and the path of movement thereof. The spring is particularly located so that it is always engaged by the driving lever and the crank arm end at their pivotal connection as the bolt moves into its fully extended position, it thereby being intended to force the driving pin into the frame slots. Again, the efficiency of this structure is questionable and unless all elements are properly formed and assembled, the security insurance described will not be provided.